I know nothing, you should listen to these guys, but...
One of my plants leaves look like that and I know what I did that made it happen, just not the chemical reason, like mag or whatever. I had one in a 1 gal pot with bottom 1/3 with water only live soil and the other 2/3 with ff. I knocked it over and just put it all back quick and without any concern but to get it back in the planter. The soil, mixed up and burned the plant. I only mention it because the leaf look is the same. I can't load it here using my phone, no matter what, it says too big. When I get home I'll upload it.
I'm pretty sure my anecdotal input has no bearing, but I thought I'd mention it